Generally, coated cutting tools whose body is made of one of tungsten carbide (hereinafter referred as WC)-based cemented carbide, titanium carbonitride (hereinafter referred as TiCN)-based cermet, and cubic boron nitride-based ultra-high pressure sintered material (hereinafter referred as cBN) are known (hereinafter collectively referred as the body). A Ti—Al-based complex nitride layer is formed by vapor deposition by a physical vapor deposition method on the body as a hard coating layer. Such coated cutting tools exhibit excellent wear resistance.
The above-described coated tools on which the Ti—Al-based complex nitride layer is formed by vapor deposition relatively excel on wear resistance. However, when they are used under a high-speed intermittent cutting condition, unusual tool failures such as chipping or the like tend to take place. Thus, several proposals were made for improving the hard coating layer.
For example, a coated tool is proposed in Patent Literature 1 (PTL 1). In the coated tool disclosed in PTL 1, a hard coating layer made of a complex nitride layer of Ti and Al is formed by vapor deposition on the surface of the body by a physical vapor deposition method. The complex nitride layer of Ti and Al satisfies 0.35≦X≦0.60 (X is atomic ratio) when the composition of the complex nitride layer of Ti and Al is expressed by the composition formula, (Ti1-XAlX)N. In addition, the hard coating layer is configured as an alternately stacked structure of a granular crystal structure and a columnar crystal structure of the (Ti, Al)N layer. Because of the configuration explained above, the hard coating layer exhibits excellent chipping resistance, fracturing resistance, and peeling resistance during high-speed intermittent cutting work of high hardness steel.
However, there is a demand for a coated tool with even more improved cutting performance since the Al content ratio X cannot be set 0.6 or higher because the hard coating layer is formed by vapor deposition by a physical vapor deposition method in this coated tool.
From the above-explained viewpoint, a proposal, in which the Al content ratio X is increased to the level about 0.9 by forming the hard coating layer by a chemical vapor deposition method, is made.
For example, formation of a (Ti1-XAlX)N layer whose Al content ratio X is 0.65-0.95 by vapor deposition by performing chemical vapor deposition in a mixed reaction gas of TiCl4, AlCl3, and NH3 at the temperature range of 650-900° C. is disclosed in Patent Literature 2 (PTL 2). What is intended in PTL 2 is improvement of the heat insulating effect by further coating the (Ti1-XAlX)N layer by the Al2O3 layer. Therefore, there is no disclosure about possible effects of forming a (Ti1-XAlX)N layer with X value increased to 0.65-0.95 on cutting performance.
In addition, for example, formation of a hard coating layer made of a (Ti1-XAlX)N layer with a cubic crystal structure is described in Patent Literature 3 (PTL 3). The Al content ratio X of the (Ti1-XAlX)N layer is 0.75-0.93. The hard coating layer is formed by performing chemical vapor deposition in a mixed reaction gas of TlCl4, AlCl3, NH3, and N2H4 at the temperature range of 700-900° C. without of usage of plasma. However, as in PTL 2, there is no disclosure in PTL 3 about its possible application as a coated tool.